1.Field of the Invention
This invention relates to a method of exposing a photo-curing type resin to light, an apparatus therefor, and a method of fabricating a printed circuit board by use of the exposing method.
2.Description of the Prior Art
In order that an ultraviolet-curing type ink may be applied to a surface of a printed circuit board to be hardened, the printed circuit board to which the ink has been applied is conventionally be carried by a conveyor. The printed circuit board is exposed to ultraviolet light from ultraviolet lamps during the conveyance.
The above-described method has the following drawbacks. First, radiant heat from the ultraviolet lamps increases a temperature of the ink, resulting in occurrence of air bubbles in the resin. The air bubbles sometimes reside as voids in the hardened resin.
Second, the increase in the temperature of the ink exposed to the ultraviolet light promotes or hastens hardening. This causes bridging density more than required and accordingly, excessively increases the hardness of the ink. When the hardness of the hardened ink is excessively increased, difficulty accompanies a step of grinding the hardened ink.
Third, when the ink is screen-printed on the printed circuit board, for example, an atmospheric pressure is merely applied to the ink after the screen printing. Accordingly, minute air bubbles contained in the ink during the screen printing cannot sufficiently be eliminated. The ink is thus hardened with the minute air bubbles contained therein.